I'm struggling to find a decent explanation for a student on the following:
'The test is really hard.' (we use definite article to specify which test, assuming listener knows which one we mean). But...
'This is A really hard test.' (we can't use the definite article in this statement and it would look very wrong, but I can't explain why).
Secondly, article rules say that mountains and rivers, lakes etc take the definite article (Eg we went camping in the Dordogne), but we would say "Mount Hood is A volcano". Again, although as a native speaker I understand it myself, I'm unable to explain to the student why this is, in a way that he will understand. He is pre-intermediate and I am used to teaching B2/C1 level learners who rarely ask me such questions!
Any help much appreciated :)